To achieve a high efficiency of separation in liquid chromatography, metallic columns (tubes) are used which are packed with finely grained sorbents. A solvent flows through the column during the chromatographic process, usually under a considerable pressure. Stainless steel is the most widely used material for the manufacturing of the columns, this warrants good mechanical properties of column, a sufficient resistance to pressure, and also in most cases, satisfactory resistance to corrosion, which may be caused by liquids applied as mobile phases or also by analyzed compounds. The columns are sealed with gaskets made of metal or of a suitable plastic material. The design of sealing fittings has to warrant minimum dead volume at the inlet and outlet ends of the column and the absence of an undesirable spreading of the sample by the flowing liquid during the chromatographic process.
Numerous designs exist for this purpose which meet the requirements mentioned above, but which also exhibit some negative effects in the liquid chromatography following in principle from the conception and material which have been used until now.
In the first place, the application of metallic columns is limited by the corrosion resistance of the material itself (stainless steel), which is very good in most organic solvents but unsatisfactory in a long-termed contact with organic acids, halogenated hydrocarbons, and their decomposition products. The metallic columns are substantially less resistant to the action of aqueous solutions of acids and salts commonly used in the reversed-phase chromatography, ion-exchange chromatography, and affinity and gel chromatography of biopolymers. Moreover, irreversible changes of the sample may take place during the contact of metal with mixtures of sensitive biologically active compounds, which are still more often separated by liquid chromatography.
The problems with the precise machining of metallic materials are of similar importance, because most of the common column designs are relatively complex. A high-quality polish of the inner surfaces of the tubes is the essential condition for the successful packing and use of columns. These facts are manifested by the relatively high production cost of the manufacturing of metallic columns. The usual design has in most cases a single-purpose manner of use and a limited life. The whole column has to be replaced if the chromatographic regime is varied or if its efficiency decreases.
The design principle analogous to that for metallic columns was also utilized in the manufacturing of glass columns (e.g. Czechoslovak Certificate of Authorship No. 183,468). Glass columns have numerous advantages in liquid chromatography, their main advantage being their high chemical resistance to the action of aggressive mobile phases or separated compounds. The high quality of the inner surface of glass tubes is of similar importance, because it reduces to a minimum the spreading of zones caused by any unevenness of the inner surface. On the other hand, the considerable brittleness of glass, its low pressure resistance, and the necessity of the shaping of glass columns for the setting of sealing fittings make difficult the utilization of recently known constructions of glass columns in high-performance liquid chromatography. Designs using a metallic jacket for the compensation of the inner pressure in the column by the outer pressure are rather demanding and expensive.